Antenna tracking refers to alignment of an antenna main beam with a satellite (or other moving object) being tracked. For example, antenna systems that are used to receive information from and/or transmit information to a satellite in a low earth orbit should be able to follow the dynamics of the satellite in its orbital trajectory. Referring to FIGS. 1A and 1B, the trajectory dynamics for an example high elevation angle pass 200 (illustrated in FIG. 2) are most pronounced in the azimuth coordinate, and the elevation variations are substantially lower. The specific conditions for these numerical values are a 450 nmi polar orbiting satellite altitude, as used by meteorological satellites, and the maximum elevation angle is 85° for this example. While these dynamics for the required antenna motion are presented for a specific case, the general characteristics for low earth orbit satellites are illustrated. The dynamics required to track the satellite are most severe in the azimuth plane, and these dynamics increase with decreasing orbital altitude and increasing maximum elevation angle. The problem of tracking a satellite at high elevation angles becomes more severe when large high gain antennas having a narrow beamwidth are employed.
Prior approaches to addressing this problem involve mechanically tilting the antenna away from the normal so that the high elevation angle travel required by the positioner is removed. In practice, both a fixed wedge angle and a third axis have been used. However, these mechanical techniques can be complex and/or costly. Furthermore, the expenses of positioner drive power and antenna stiffness needed for the dynamic motion are incurred when high antenna dynamics are required.
Thus, it would be useful to be able to provide an antenna-tracking alternative to the prior mechanical approaches. It would also be desirable to be able to provide less complex and/or costly antenna tracking.